1. Field of the Invention
The invention relates to a torque-measuring arrangement of a gear drive for transmitting a rotary movement and the power of which is transmitted via helically toothed spur gears.
Known torque-measuring arrangements comprise a measuring shaft provided in the gear train of a gear drive for the transmission of power. Two transducers measuring the torsion angle of the measuring shaft are assigned to said measuring shaft at a defined axial distance, said torsion angle being proportional to the torque to be measured.
In the DE-OS 28 15 463 A1 and in the patent publications DE 31 12 714 C1, FR 1 596 833 and GB 644 234 two respective measuring gears are mounted on the measuring shaft at the above-mentioned distance; in addition to measuring purposes, said gears may be used for the transmission of power. When passing a sensor, the teeth of the measuring gears initiate electrical pulses the respective torque-dependent phase shifting of which is determined in an evaluation device.
The patent publication DD 257 488 also describes an arrangement operating according to the differential-angle principle, an arrangement in which a respective rotary encoder is connected to each shaft end in order to determine the torsion angle of a drive shaft.
Disadvantageous with these solutions is that the sensors directed onto the teeth of the measuring gears require additional mounting space in radial direction, and that the torque-dependent phase shifting is determined as a function of speed, which increases the efforts in the evaluation device, and that the sensitivity and accuracy of the measuring arrangement depends from the number and the pitch accuracy of the measuring gears or may be improved by means of a measuring shaft being of little torsional stiffness, which is limited by the power to be transmitted and the thus increased tendency to vibrate.
Further known torque-measuring devices operate with force-measuring devices, in particular strain gauges, which are are provided in a measuring bearing or directly in the toothing of the power-transmitting drive gear (DE 25 26 582 C2). Said devices have the disadvantage that the stiffness of such measuring bearings is smaller than that of conventional bearings requiring the same mounting space. Furthermore, the stiffness of the frames receiving the measuring bearings is reduced as a result of the larger mounting space needed for the measuring bearings so that, in general, the integration of measuring bearings brings about disadvantageous changes with respect to the dynamic gearing properties.